JP4019134B2 - Plastic molding method and molding die - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plastic molding method and a molding die, and particularly to a molding method and a molding die for optical elements such as a plastic lens having a highly accurate mirror surface and a plastic mirror.
[0002]
[Prior art]
Optical elements such as rectangular lenses or mirrors having laser beam imaging and various correction functions are used in optical writing units of laser-type digital copying machines, printers, or facsimile machines. In recent years, these optical elements have changed from glass to plastic due to demands for cost reduction of products, and since a plurality of functions are provided with minimum elements, the transfer surface shape is not only spherical but also complicated It has come to have a spherical shape.
[0003]
In the case of a lens, the shape of the lens is increasing in thickness and the thickness is not uniform in the longitudinal direction. In addition, the manufacturing method is low in manufacturing cost, and an injection molding method suitable for mass production, or the insert forming the transfer surface arranged in the mold can be moved (movable insert), and the mold can be moved into the mold. It is common to use a so-called injection compression molding method in which the movable insert moves forward with respect to volume shrinkage accompanying cooling of the filled resin to ensure the shape accuracy by compensating the pressure.
[0004]
When manufacturing a lens by such an injection molding method or an injection compression molding method, the resin pressure or resin temperature in the mold is changed in the process of injecting and filling the heat-melted resin material into the mold and cooling and solidifying it. Uniformity is desirable to ensure the desired shape accuracy.
[0005]
However, when the lens thickness is uneven, the cooling rate of the filled resin differs depending on the lens thickness deviation, resulting in differences in volume shrinkage, resulting in poor shape accuracy or lens thickness. There was a problem that "sinks" occurred in thick areas. In the case of a thick wall, sinking is likely to occur due to a large volume shrinkage during the resin cooling process. If the injection pressure is increased to prevent sinking (increasing the resin filling amount), internal distortion will occur. May have an adverse effect on optical performance.
[0006]
In addition, when manufacturing using the injection compression molding method, it can be molded at a lower injection pressure than the injection molding method, but if there is a deviation in the lens thickness, the volume shrinkage will be reduced at each part in the longitudinal direction. There is a difference, and this makes it impossible for the movable nest to follow the volume shrinkage of the resin and cannot apply an equal pressure. It was.
[0007]
Japanese Unexamined Patent Publication No. 11-28745 discloses a molding method in which the disadvantages of the injection molding method or the injection compression molding method are improved. 7A and 7B relate to the mold 100 used in this molding method, wherein FIG. 7A is a front sectional view showing the main structure, and FIG. 7B is a front sectional view for explaining the operation.
[0008]
In the molding method, as shown in FIG. 7A, after filling the mold 100 with the molten resin, the cavity piece (sliding piece) as shown in FIG. 7B during cooling to a temperature lower than the softening temperature. ) 102 is separated from the resin 101a in the cavity, thereby defining a gap 110 between the sliding piece 102 and the resin. In this molding method, shrinkage caused by cooling is absorbed by the movement of the resin facing the gap, and sinking is prevented from occurring on the transfer surface by preferentially sinking the resin facing the gap. .
[0009]
By the way, in this molding method, when the molten resin is filled into the cavity 101, the cavity piece 102 is separated by a force that does not lose the resin pressure during filling [in the direction of the thick arrow in FIG. 7A]. It is necessary to press and fix. At this time, the other cavity pieces 103 to 106 are also pressed with the same large force (direction of thin arrows in FIG. 7A) via the cavity pieces 102 to be separated.
[0010]
As a result, when the pressing force is released in order to separate the cavity piece 102 from the resin (in the direction of the thick arrow in FIG. 7B), the other fixed cavity piece 103 that has been pressed so far. -106 are simultaneously released from the pressing (in the direction of the thin arrow in FIG. 7B), causing a problem of moving. If there is even a slight error in the machining error or assembly position accuracy of the cavity piece or other mold member that fixes the cavity piece, the movement of the cavity piece cannot be completely suppressed.
[0011]
In the molding method, since the cavity piece 102 needs to be separated from the resin (the pressing force is released) before the resin is completely solidified, the cavity pieces 103 to 106 move even slightly when separated. Then, partial separation of the resin occurs from the cavity surfaces of the cavity pieces 103 to 106, and sink marks grow due to shrinkage accompanying cooling of the resin from there. In other words, there is a problem that sinks occur in undesired places.
[0012]
[Problems to be solved by the invention]
The present invention has been made in view of the above points, and its purpose is to suppress the occurrence of sink marks on the transfer surface, and to enable plastic products with high transfer accuracy to be manufactured with high productivity in a short molding cycle. It is an object to provide a molding method and a molding die.
[0013]
[Means for Solving the Problems]
The plastic molding method according to claim 1 (see FIGS. 5 and 6 ) includes a plurality of cavities including a slidably provided cavity piece (sliding piece) and a fixedly arranged cavity piece (fixed piece). An injection mold that defines a cavity composed of surfaces and at least one of these cavity surfaces as a transfer surface and transfers the transfer surface to the resin by the resin pressure generated in the cavity is a softening point temperature of the resin. After the molten resin is injected and filled into the cavity while being held at a temperature lower than the temperature, the sliding piece is slid away from the resin in the cavity while the molten resin is cooled to a temperature lower than the softening temperature. In the plastic molding method in which a gap is formed between the surface and the resin in the cavity, in the injection filling step, the sliding piece is caused by the resin pressure generated in the cavity. So as not to slide in the direction of the space formed, is fixed by applying a pressing force to the sliding piece, the pressing force so as not extend to the fixed piece, further the injection filling process, the sliding This is performed in a state where the cavity surface of the moving piece does not come into contact with the fixed piece and a gap is formed between the front end surface of the sliding piece and the fixed piece .
[0014]
A molding method according to a second aspect (see FIGS. 5 and 6 ) is characterized in that the gap is 50 μm or less in the first aspect.
[0015]
The molding method according to claim 3 is characterized in that, in the injection filling step according to claim 1 or 2, the cavity surface of the sliding piece is brought into contact with a part of the side surface of the resin in the cavity and is not brought into contact with the fixed piece. To do.
[0016]
The molding method according to claim 4 (see FIG. 5) is the method according to claim 1, wherein the sliding piece is slid by a pressing device provided outside the mold, and the sliding piece in the injection filling process is The fixed position is controlled by a stroke amount of a pressure control mechanism that controls the operation of the pressing device.
[0017]
The molding die according to claim 5 ( see FIG. 6) is composed of a plurality of cavity surfaces by a slidably provided cavity piece (sliding piece) and a fixedly arranged cavity piece (fixed piece). The cavity is defined, and at least one of the cavity surfaces is used as a transfer surface, and the sliding piece is slid away from the resin in the cavity while the molten resin is injected and filled in the cavity and then cooled. Thus, in the plastic injection mold in which a gap is formed between the cavity surface of the sliding piece and the resin in the cavity, a pressing force opposite to the direction of the gap formation is applied to the sliding piece. And a structure in which the sliding piece does not come into contact with the fixed piece when the pressing force is applied, and further comes into contact with the forward part of the sliding piece in the sliding direction when the sliding piece moves forward. Or providing a timber, or a contact portion is formed, characterized in that so as to form a gap between the abutment by the front end surface of the sliding piece and the fixing piece.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[Reference Example 1]
1 and 2 are drawings of Reference Example 1, and FIG. 1 shows a structure of a main part of a molding die and a state when molten resin is injected and filled into the die, and (a) is a front view. Sectional drawing and (b) are the AA sectional views (side sectional drawing). FIG. 2 is a front sectional view for explaining the function of the mold.
[0021]
In FIG. 1A, the mold 10 is slid on the upper mold 11, the lower mold 12, cavity pieces (fixed pieces) 6 and 7 a to 7 d fixed between them, and the fixed piece 6. A cavity piece (movable telescope or sliding piece) 13 that is freely inserted and a pressing device 4 that applies a predetermined pressing force to the sliding piece 13 are configured. The cavity 1 is defined by the fixing pieces 6 and 7a to 7d and the sliding piece 13, and is formed by the fixing piece 7a among a plurality of cavity surfaces (surfaces on which the fixing piece and the sliding piece face the cavity 1) ( The surface on which the fixing piece 7a faces the cavity 1) is the transfer surface 2 for transferring the mirror surface to the molded product, and all other cavity surfaces are non-transfer surfaces.
[0022]
As shown in FIGS. 1A and 1B, the entire front end surface of the sliding piece 13 is a cavity surface (reference numeral 5 is a molding surface formed by the sliding piece 13), whereas the fixed piece 6 has a front end surface thereof. Part of the cavity surface. Further, the front end surface of the sliding piece 13 is configured not to contact any of the fixed pieces 7a to 7d. The pressing device 4 is for applying a pressing force to the sliding piece 13 and fixing it so that the sliding piece 13 does not slide leftward in FIG. 1 due to the resin pressure generated in the cavity 1. For this, a pressure control mechanism is provided. Further, this mold is provided with an unillustrated sprue, runner, gate, eject pin, and the like as in a normal injection mold.
[0023]
Next, a plastic injection molding method using the molding die will be described. The mold is clamped to the state shown in FIGS. 1A and 1B (however, the resin is not injected and filled in the cavity 1). Next, the entire mold is held at an appropriate temperature lower than the softening temperature of the resin, and in this state, the molten resin is injected and filled into the cavity 1, and the transfer surface 2 is transferred to the molded product by the resin pressure generated in the cavity. A molded product is obtained by cooling and solidification.
[0024]
In this injection filling process, the shape and volume of the cavity 1 are kept constant. For this purpose, it is necessary to fix the position so that the sliding piece 13 is not moved by being pressed by the pressure of the resin in the cavity. Therefore, in this embodiment, a pressing force in the forward sliding direction is applied from the pressing device 4 to the sliding piece 13. The magnitude of the pressing force is set and maintained at a value equal to or greater than the maximum resin pressure generated in the cavity when the resin is injected and filled into the cavity 1 by the pressure control mechanism.
[0025]
When the cooling of the resin 1a in the cavity 1 proceeds and the pressure reaches a predetermined value, the sliding piece 13 is slid backward as shown in FIG. 2 by the pressing device 4 (the direction of the arrow in FIG. 2). ), A predetermined gap 18 is formed between the front end face of the sliding piece 13 and the resin 1a in the cavity. With the void 18 formed, the resin 1a in the cavity is cooled to an appropriate temperature lower than its softening temperature, and then the mold is opened to take out the molded product.
[0026]
Unlike the other resin portions, the resin portion facing the void 18 does not have an adhesive force with the molding surface of the cavity 1 (the cavity surface). Since the portion is contracted and deformed preferentially over the resin portion in contact with the transfer surface 2 and the resin portion in contact with the fixing pieces 7b to 7d, sink marks (concave or convex shape) Instead, sink marks in the resin portion that contacts the cavity surface such as the transfer surface 2 are suppressed, and as a result, the desired transfer surface can be faithfully transferred. Thus, it is possible to obtain a molded product with very high transfer accuracy in a short molding cycle.
[0027]
In the mold of the above form, the sliding piece 13 is slidably inserted into the fixed piece 6 as shown in FIG. Unlike the conventional mold shown in FIG. 7, the front end surface of the sliding piece 13 does not come into contact with other fixed pieces (including those having a mirror surface portion). For this reason, according to this mold, when the position of the sliding piece 13 is fixed in the resin injection filling process, the pressing force applied from the pressing device 4 to the sliding piece 13 reaches the fixing pieces 7b to 7d. There is nothing. As a result, even if the sliding piece 13 is slid backward (FIG. 2) as described above before the resin is completely solidified, these fixing pieces do not move. It is possible to prevent a problem that peeling occurs and sinks occur in an undesirable portion.
[0028]
[Reference Example 2]
FIG. 3 is a side sectional view showing the main structure of the molding die and the state when the molten resin is injected and filled into the die. This mold is a modification of the mold shown in FIG. That is, when the area of the transfer surface 2 becomes large in the mold of FIG. 1, the area for guiding the sink of the gap-facing resin portion (this corresponds to the front end of the sliding piece 13 in FIG. 1). It is necessary to increase the surface, that is, the area of the cavity surface of the sliding piece 13). Therefore, the mold according to the present embodiment is such that the cavity surface of the sliding piece 23 has a shape similar to the side surface shape of the cavity and is made as large as possible, as shown in FIG.
[0029]
[Reference Example 3]
FIG. 4 is a side sectional view showing the main structure of the molding die and the state when the molten resin is injected and filled into the die. This mold is also a modification of the mold of FIG. 1, and the purpose of the modification is to deal with the case where the area of the transfer surface 2 in the mold of FIG. In addition, a large cavity surface is secured by projecting and arranging a large number of pins 33 a in front of the sliding piece 33. The multi-pin type sliding piece 33 is effective when it is difficult to insert a sliding piece similar to the side shape of the cavity because of its complicated shape.
[0030]
Based on the contents described in the above reference examples 1 to 3, embodiments of the present invention will be described below with reference to the drawings.
[First Embodiment]
FIG. 5 is a front sectional view for explaining the main structure of the molding die and the operation of this die. In this mold, the sliding piece 43 having a large front end surface area is slidable with respect to the upper die 11 and the lower die 12 (reference numeral 20 is a sliding surface), and part of the front end surface is a cavity surface. It is what. And in the injection filling process of resin in this metal mold | die, as shown in FIG. 5, after making the sliding piece 43 slide by the press apparatus 4, the position is fixed, The front end surface of the sliding piece 43 A gap 19 having a predetermined dimension is formed between the fixing pieces 7a and 7c. While maintaining this state, the cavity 1 is injected and filled with molten resin.
[0031]
When the cooling of the resin in the cavity 1 proceeds and the pressure reaches a predetermined value, the sliding piece 43 is slid backward by the pressing device 4, and the gap between the front end surface of the sliding piece 43 and the resin in the cavity is reached. A predetermined gap is formed (not shown). With this void formed, the resin in the cavity is cooled to an appropriate temperature lower than its softening temperature, and then the mold is opened to take out the molded product.
[0032]
5 has a structure in which the front end surface of the sliding piece 43 does not come into contact with the fixed pieces 7a and 7c, the pressing force from the pressing device 4 for fixing the position of the sliding piece 43 is fixed. Since it does not reach 7a-7d, the effect similar to the metal mold | die of FIG. 1 is acquired. Further, in the mold of FIG. 1, the entire front end surface of the sliding piece 13 is a cavity surface (a part thereof), so that the sliding surface of the sliding piece 13 with respect to the fixed piece 6 is exposed to the cavity 1 ( In contrast to FIG. 2, in the mold of FIG. 5, a part of the front end surface of the sliding piece 43 is a cavity surface, so that the sliding surface 20 of the sliding piece 43 is not exposed to the cavity 1. . As a result, it is not necessary to increase the accuracy of the outer shape of the sliding piece 43, and the problem of “galling” of the sliding portion does not occur.
[0033]
The size of the gap 19 shown in FIG. 5 is preferably 50 μm or less, so that it is possible to prevent “burrs” from being generated in the gap 19 during resin injection filling. In order to set the size of the gap 19 to a desired value, the stroke amount of the pressure control mechanism provided in the pressing device 4 may be adjusted, and the clearance 19 can be easily executed without requiring a special mechanism.
[0034]
[Second Embodiment]
FIG. 6 is a front sectional view for explaining the main structure of the molding die and the operation of this die. This mold is obtained by modifying the mold shown in FIG. 5 to simplify the structure for setting the size of the gap 19 at the time of resin injection filling to a desired value. That is, in the lower mold 12, a projection 21 that abuts the sliding piece 53 when the sliding piece 53 slides is formed at a front portion in the sliding direction of the sliding piece 53, and the sliding piece 53 that slides forward contacts the projection 21. By stopping, the gap 19 is formed. It is possible to change the size of the gap 19 by adjusting the size of the projection 21 or the size of the sliding piece 53 in the sliding direction.
[0035]
【The invention's effect】
As is apparent from the above description, the present invention provides the following effects.
(1) Since the pressing force for fixing the sliding piece does not reach the fixing piece, there is no problem that the fixing piece moves when the sliding piece is separated from the resin in the cavity. As a result, it is possible to prevent sink marks due to partial separation of the resin from the cavity surface of the fixed piece, and the cavity surface of the sliding piece does not come into contact with the fixed piece in the injection filling process. The effect is obtained because the pressing force for fixing the moving piece does not reach the fixed piece.
Moreover, the shaping | molding method which can acquire the said effect can be implemented, without requiring a complicated mechanism and structure.
( 2 ) Further, since the injection filling process is performed in a state where a gap of 50 μm or less is formed between the front end face of the sliding piece and the fixed piece, a “burr” is generated in the gap during resin injection filling. Can be prevented.
( 3 ) Furthermore, since the size of the gap is set by adjusting the stroke amount of the pressure control mechanism, the size of the gap can be easily maintained at a desired value without requiring a special mechanism. can do.
[Brief description of the drawings]
[0036]
FIGS. 1A and 1B show a structure of a main part of a molding die according to Reference Example 1 and a state when a molten resin is injected and filled into the die. FIG. 1A is a front sectional view, and FIG. It is an AA line sectional view (side sectional view).
FIG. 2 is a front sectional view for explaining the operation of the mold of FIG. 1;
FIG. 3 is a side sectional view showing a main part structure of a molding die according to Reference Example 2 and a state when molten resin is injected and filled into the die.
FIG. 4 is a side cross-sectional view showing a main part structure of a molding die according to Reference Example 3 and a state when molten resin is injected and filled into the die.
FIG. 5 is a front sectional view for explaining the main structure of the molding die according to the first embodiment and the operation of the die.
FIG. 6 is a front cross-sectional view for explaining the main structure of a molding die according to a second embodiment and the operation of this die.
7A and 7B are related to a conventional molding die, in which FIG. 7A is a front sectional view showing a main part structure, and FIG. 7B is a front sectional view for explaining the operation.
[Explanation of symbols]
[0037]
DESCRIPTION OF SYMBOLS 1 Cavity 1a Resin in cavity 2 Transfer surface 4 Pressing device 5 Molding surface 6 Fixing piece (cavity piece)
7a-7d Fixed piece (cavity piece)
10 Mold 11 Upper mold 12 Lower mold 13 Sliding piece (cavity piece)
DESCRIPTION OF SYMBOLS 14 Pressing device 18 Cavity 19 Crevice 20 Sliding surface 21 Protrusion 23 Sliding piece 33 Sliding piece 33a Pin 43 Sliding piece 53 Sliding piece 100 Mold 101 Cavity 101a Resin in cavity 102 Sliding piece (cavity piece)
103-106 Fixed piece (cavity piece)
110 gap

Claims (5)

A cavity piece (sliding piece) provided slidably and a cavity piece (fixed piece) fixedly arranged define a cavity composed of a plurality of cavity surfaces, and at least one of these cavity surfaces is defined as a transfer surface. None, the injection mold that transfers the transfer surface to the resin by the resin pressure generated in the cavity is held at a temperature lower than the softening point temperature of the resin, and the molten resin is softened after injection filling the cavity. In the plastic molding method of forming a gap between the cavity surface of the sliding piece and the resin in the cavity by sliding the sliding piece away from the resin in the cavity while cooling to below the temperature,
In the injection filling process, the sliding piece is fixed by applying a pressing force so that the sliding piece does not slide in the direction of the gap formation due to the resin pressure generated in the cavity. Do not reach the fixed piece,
Further, the injection filling step is performed in a state where the cavity surface of the sliding piece does not contact the fixed piece and a gap is formed between the front end surface of the sliding piece and the fixed piece. Molding method.   The molding method according to claim 1, wherein the gap is 50 μm or less.   3. The molding method according to claim 1, wherein, in the injection filling step, the cavity surface of the sliding piece is brought into contact with a part of the side surface of the resin in the cavity and is not brought into contact with the fixed piece.   The sliding piece is slid by a pressing device provided outside the mold, and the fixed position of the sliding piece in the injection filling process is controlled by a stroke amount of a pressure control mechanism that controls the operation of the pressing device. The molding method according to any one of claims 1 to 3. A cavity piece (sliding piece) provided slidably and a cavity piece (fixed piece) fixedly arranged define a cavity composed of a plurality of cavity surfaces, and at least one of these cavity surfaces is defined as a transfer surface. None, while the molten resin is injected and filled into the cavity and then cooled, the sliding piece is slid away from the resin in the cavity to create a gap between the cavity surface of the sliding piece and the resin in the cavity. In plastic injection molds that are designed to form,
While providing a pressing device that applies a pressing force in the direction opposite to the direction of the gap formation to the sliding piece, the sliding piece does not contact the fixed piece when the pressing force is applied,
Further, a contact member that abuts when the sliding piece advances and slides is provided at a front portion in the sliding direction of the sliding piece, or a contact portion is formed, and the front end surface of the sliding piece and the fixing piece are formed by the contact A molding die characterized in that a gap is formed between the two.

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